Abstract
The roles of microstructure in plastic deformation and crack growth mechanisms of a titanium alloy with a trimodal microstructure have been systematically investigated. The results show that thick intragranular α lath and a small number of equiaxed α phases avoid the nucleation of cracks at the grain boundary, resulting in branching and fluctuation of cracks. Based on electron back-scattered diffraction, the strain partition and plastic deformation ahead of the crack tip were observed and analyzed in detail. Due to the toughening effect of the softer equiaxed α phase at the grain boundary, crack arresting and blunting are prevalent, improving the crack growth resistance and generating a relatively superior fracture toughness performance. These results indicate that a small amount of large globular α phases is beneficial to increase the crack propagation resistance and, thus, a good combination of mechanical property is obtained in the trimodal microstructure.
Highlights
Due to their high strength, good corrosion and fatigue resistance, titanium alloys have been extensively used for aerospace engineering [1,2]
It deviates from the grain boundary with an angle of 58◦ when it encounters the equiaxed α phase located at the GB (Figure 4e), which improves the crack growth resistance and is beneficial to improving the fracture toughness of the microstructure. These results indicate that a small amount of equiaxed primary α phases located at the grain boundary is instrumental in the deflection and bifurcation of the main crack propagation
Based on electron backscattered diffraction (EBSD), the strain partition within the grain interior that could reduce the only confined to the grain boundary α (GB α) phase, but occurs both in the αp phase and the neighbor primary α lath
Summary
Due to their high strength, good corrosion and fatigue resistance, titanium alloys have been extensively used for aerospace engineering [1,2]. The crack growth resistance is significantly influenced by the volume fraction and size of the equiaxed α phase as well as the grain boundary [4,5,6] in bimodal microstructures and equiaxed microstructures. The propagation of microvoids can be restricted by softer coarse α particles [7] For titanium alloys, this is significantly strengthened by the fine secondary α phase [3,8]; crack growth is mainly affected by the thickness of the lamellar α phase, grain boundary α (GB α) and the α colony size of the lamellar microstructure [4,9]. The microstructure that has high fracture toughness may lead to an unsatisfactory decrease in other properties
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